Crossover from Metallic to Semiconducting in Pb2-xLnxRu2O7-δ (Ln = Eu, Sm) Compounds with Pyrochlore Structure
We study the synthesis and physical properties of Pb2-xLnxRu2O7- (Ln = Sm, Eu) compounds with pyrochlore structure. The lead-lanthanoid pyrochlores Pb2-xLnxRu2O7- (Ln = Sm, Eu) have been successfully synthesized by the solid-state reaction. All samples were characterized by X-ray diffraction, magnetic susceptibility, and electrical resistivity measurements. Magnetic susceptibility measurements showed that the spin-glass transition temperature, TSG, decreases with Ln content x and goes to zero at x = 0.2 and 0.6 for Sm and Eu, respectively. From electric resistivity measurements, a crossover from metallic to semiconducting behavior was observed in the range of 0.2 ≤ x ≤ 0.4 and 0.4 ≤ x ≤ 0.8 in Pb2-xSmxRu2O7- and Pb2-xEuxRu2O7-, respectively. These boundaries between metallic and insulating phases mostly correspond to values of x with TSG = 0. These metal-insulator transitions can be caused by the strongly correlated couplings between the itinerant 4d electrons which are possibly attributed to the magnetic frustration.
Akira Kawasaki, Akinaga Kumakawa and Masayuki Niino
K. Masaki et al., "Crossover from Metallic to Semiconducting in Pb2-xLnxRu2O7-δ (Ln = Eu, Sm) Compounds with Pyrochlore Structure ", Materials Science Forum, Vols. 631-632, pp. 483-488, 2010